Layered graphene oxide membranes functioned by amino acids for efficient separation of metal ions

Abstract

Abstract As a kind of heavy metal, lead ions (Pb2+) are a great threat to human health and the ecological environment. Due to their excellent properties, graphene and its derivatives are expected to be used for water purification. Amino acid functional groups were designed for graphene oxide membranes via dehydration condensation. The effects of the amino acid groups on the membrane performance for separating metal ions were investigated by the molecular dynamics. Under the premise that the water permeability is basically the same, the retention rate for Pb2+ by alanine groups with negatively charged terminals is 1.6 times of that by the carboxyl groups. The number-density map and the radial distribution function indicate that a large area of local high-density regions of Pb2+ will be formed around the negatively charged alanine groups. At the same time, the diffusion coefficient for Pb2+ and Na+ can be effectively reduced by the electrostatic attraction of the negative groups. It is concluded that functioned by the negatively charged alanine, the retention rate for metal ions by the layered graphene oxide membranes can be significantly improved at the cost of a little loss in water permeability.